It has been proposed heretofore (see U.S. Pat. No. 3,996,713 and the German Patent Document No. 2 514 300) to provide so-called sandwich panels or, more specifically, prefabricated multilayer steel-reinforced concrete panels with a steel-reinforced concrete outer plate, a steel-reinforced concrete inner plate, and an intermediate layer of thermal and acoustic insulating material between these plates. The plates are held together by anchors which traverse the insulating layer and are locked to the respective plates.
As will be apparent from the prior art as represented by the aforementioned patent and patent document, the anchors interconnecting the concrete plates include so-called flat anchors or membrane anchors which can comprise steel sheets or plates perpendicular to the concrete plates and affording a limited degree of relative mobility of the concrete plates.
These flat anchors are uniformly distributed along an imaginary circle whose diameter is larger than the length of the small size of the rectangular panel.
The flat anchors are membrane anchors as there described, with a generally flat configuration and are usually composed of sheet steel although it is conceivable to form the flat anchors as an assembly of rods provided that the assembly is deflectable transverse to its plane. Flat anchors are thus elastically deformable and constitute membrane connections at spaced-apart locations along this circle between the two reinforced-concrete plates. The portions of the flat anchors embedded in the reinforced-concrete plates are statically connected to the reinforcing steel, e.g. mats, of the reinforced concrete plates.
However, in spite of the unique advantages of sandwich panels of the aforedescribed type and the sandwich panel constructions of the prior art mentioned in said U.S. patent, it has been found to be necessary in practice to provide an additional anchor at the centrum of the panel. At this centrum, the anchor is generally rigid and can consist of an anchor sleeve with connecting pins or rods embedded in the two concrete plates. A system which also uses a rigid anchor at the centrum is described in U.S. Pat. No. 3,757,482 and German Patent Document No. 20 08 402. In the latter system hairpin-like anchors are provided.
The flat anchors can be traversed by rods which are embedded in the reinforced concrete of the two plates and may be welded, if desired, to the reinforcing mats thereof.
The provision of a rigid anchor at the centrum of the panel has been found to be expensive and undesirable from a static viewpoint since this anchor must not only be capable of withstanding the resultant forces of this centrum, but must accommodate the thermal expansion, and shrinkage effects which invariably arise. The presence of a rigid anchor at the centrum interferes and may result, in turn, in undue stress upon the concrete plates.
Furthermore, it has been recognized that it is of advantage to allow for relative shifting of the two plates parallel to themselves to a limited degree and even this has been unduly restricted by the additional rigid member at the anchoring centrum.